Request advice: identifying a cable

[mark641]

Today I had to PAT a microwave oven. All seems well, except it is wired in thin-looking cable:

cable: 5.5 mm dia
N wire with insulation 1.8
Bare wire, twisted, 0.7

Please am I right that this is 3 amp cable? The oven is a Proline ST22, rated 1200 watt; the
plug has a 13A fuse; the cable has no identifying marks.

I assume that strictly speaking whenever you PAT something, you should check the cross-section
area of the wires: are they fat enough to carry the rated current of the fuse? But I have no idea
how to do so.

 

[Fazz711]

CSA of cable is Pye r square X the number of strands

 

[mark641]

CSA of cable is Pye r square X the number of strands

Thank you. Unfortunately this formula is difficult to apply because you must count the strands & measure r which is the radius of 1 strand. I was hoping there was some rule-of-thumb like "a 1.0 mm^2 wire, twisted
is about 1.5 mm diameter". The formula: CSA = Pi r^2 is only valid for solid wires.

 

[snowhead]

What does the spec stamped on the flex outer sheath say?

Appliance Manufacturers quite often use flex, in short lengths, that appears to be undersized.

For example my kettle has a flex marked HO5VVF 3 x 1.0mm², that would appear to be undersized as the kettle is 3kw and the flex is generally rated at 10amp.
But as the Kettle was bought direct from Morphy Richards in the U.K a few months ago I doubt there is anything to be concerned about.

 

[Marvo]

Unless it's marked on the cable you're always going to struggle to calculate an accurate CSA with a fine stranded flexible trailing cable due to the difficulties in measuring the diameter of the individual strands.

If it's the OEM cable that was supplied with the microwave I wouldn't second guess its suitability unless there's signs of thermal deterioration such as reduced flexibility. If you want to be on the side of caution you could run the microwave for a few minutes and use a thermal camera to see if the cable is getting significantly warm, if the temp increases more than 15 or maybe 20 degrees C above ambient it might be worth further investigation.